(a) Technical Field
The present disclosure relates to a fuel cell stack with a multilayer type collector plate, and more particularly, to a fuel cell stack capable of manually increasing the temperature of cells arranged proximate to an end plate of the stack to improve starting performance of a fuel cell vehicle at temperatures below zero and driving performance thereof at low temperatures.
(b) Background Art
In general, a fuel cell stack includes a plurality of unit cells configured to generate electricity, end plates which are disposed on both sides of the stacked unit cells to fixedly support the unit cells, and current collector plates which are disposed inside the end plates to collect electricity generated by the unit cells and to transmit the same to the outside.
Meanwhile, FIG. 6 illustrates a cell temperature profile when a fuel cell stack is operated according to the related art. As illustrated in FIG. 6, a cell disposed at the center of the stack has the highest temperature, and cells disposed at both ends of the stack adjacent to end plates (hereinafter, referred to as “end cells”), have relatively low temperatures. When the stack is operated, the temperature of each cell increases by the exothermic reaction thereof. However, the temperature of each end plate, made of stainless and plastic, is relatively low since a thermal loss from the end plate is greater than from the central portion of the stack due to the influence of outside air (or atmospheric air), with the consequence that generated water remains therein and therefore the voltage of each end cell is reduced.
In particular, when the temperature of the end cell is less than the operating temperature of the stack, the voltage of the cell is reduced due to the flooding of the cell, deterioration of the activation energy thereof, etc. As a result, the performance of the stack is reduced, and cell degradation occurs since electrodes are damaged when cell performance is reduced for a long period of time, which leads to a reduced lifespan of the stack. When the reduction in voltage of a specific cell is greater in a fuel cell vehicle, shut-down logic is typically applied to the vehicle. Therefore, a driver may be faced with unexpected situations when driving the vehicle.
Particularly, it is necessary to improve reliability of operation of the fuel cell stack by uniformly distributing the cell temperature to maintain the temperature of the end cells to be the same as that of all of the cells in the stack under a sub-zero starting condition during the winter season, in which generated water may freeze, or a low-temperature operation condition. Accordingly, a system has been developed in the related art in which the temperature between an end plate and an end cell is increased to prevent the cell temperature from being decreased in the vicinity of the end plate.
For example, the related art discloses a technology in which a structure for circulating high-temperature coolant discharged from a stack is applied to an end plate to prevent the temperature of a cell disposed at the end of the stack from being lowered. In another example, the related art discloses a technology for combusting and heating a hydrogen-air mixture in a compartment within a terminal plate, as a heating means for thawing during the cold startup of a stack. However, in the related art, when coolant is not circulated to increase the temperature of the cell when the stack is started at temperatures below zero, the end cell may not be substantially heated. In addition, since hydrogen is combusted in the compartment within the terminal plate for thawing the end cell during the cold startup of the stack, it is disadvantageous in terms of use of hydrogen and vehicle fuel efficiency, and there is a safety problem relating to the removal of hydrogen remaining in the compartment within the terminal plate, in which a high electric potential is formed.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.